The present invention relates to a radio modem for modulating and demodulating data to be interchanged between remote data terminals and, more particularly, to a radio modem implemented as an IC (Integrated Circuit) card.
A conventional IC card radio modem for the above application has a communication interface circuit. When the radio modem is connected to a personal computer or similar data terminal matching it as to communication access conditions, it allows the data terminal to interchange data with a remote data terminal. Usually, the type of an IC for controlling a serial port differs from one data terminal to another data terminal. Hence, the communication access conditions of the conventional radio modem match only a single kind of data terminals. This brings about a problem that the radio modem does not allow two or more different kinds of data terminals to communicate, i.e., it is applicable only to, for example, PC-AT based data terminals.
In today's sophisticated business environments, there is an increasing demand for mobile computing services which allow computing resources to be accessed from data terminals located at destinations. For example, mobile computing allows a person to access a data base or similar computing resource by using a data terminal located at a client's office. However, with the conventional IC card radio modem, the person cannot operate the data terminal for communication unless the data terminal matches the radio modem. Therefore, the radio modem cannot meet the demand for "communication at any time and any place" services.
Japanese Patent Laid-Open Publication No. 64-60049 discloses a system in which a plurality of different modems are built in a local switch, and one of them matching the modem of a maintenance company is automatically selected. However, this system is not practicable without resorting to a local switch and a plurality of modems which increase the cost.